A fuel injector known in the art comprises a cylindrical body in which a needle is arranged sliding axially between an open position allowing the injection of fuel into a combustion chamber and a closed position preventing said injection. The movements of the needle are hydraulically controlled by a control valve comprising a fixed coil working with a magnetic armature that can be moved between an open position reached when the coil is energized, a position likewise referred to as the “up” position or position close to the coil, and a closed position or a “down” or “remote” position reached when the coil is no longer energized.
The overall shape of the armature is that of a stylized mushroom, the cap of which would be formed by a magnetic circular plate and the foot by a rod forming the valve piston. The plate is arranged proximate to the coil and the piston extends from the center of the plate, moving away from the coil.
When the coil is not energized, the armature is pushed back into the closed position by a compression spring arranged between the plate and the coil. Fuel at high pressure is then captive in a control chamber and it applies a closing force to the needle, keeping it in the closed position.
When the coil is energized, it attracts the magnetic plate towards the up position and opens a discharge channel through which the captive fuel in the control chamber can escape, the pressure in said chamber dropping to allow a needle to move into the open position.
The fuel that has escaped from the control chamber occupies the entire volume available around the armature and is found particularly in the space between the coil and the magnetic plate where it can interfere with the armature movements.